If you’re an Amateur Radio operator and enjoy designing and building your own antennas, like I do. This 6m Slim Jim antenna is a very gratifying project, and cheap too.
The 6 Meter Ham band covers 50-51 MHz. Using an online Slim Jim calculator to get the proper dimensions, assume the Velocity Factor (Vf) = 0.9 for 450 Ohm Ladder. At 50 MHz this makes for an antenna about 20 feet tall.
The diagram below shows the various elements (A-F) calculated above.
According to the diagram above the E Gap (6cm, 2.4″) is longer than the ladder insulated window 2″. This means that the bottom portion of the antenna would be supported by a single 18AWG wire and would bend awkwardly if mounted vertically. To support both sides of the Ladder, I cut out a 2″ plastic section of Ladder line and Bonded over the insulation void 1.25″ to fill the Gap and support both Right and Left sides of the antenna.
By Bonding I mean using a particular Locktite Plastics Bonding Glue, generally available in your local Building Supply store. This plastic bonding joint has held up outdoors for more than a decade.
The Choke Balun shown below is constructed of Snap-on Ferrite beads and Shireen RFC100A coaxial cable, 6 feet length. NanoVNA measurements indicated this Balun had no adverse effect on VSWR.
The finished antenna standing tall in the backyard. I was able to make SSB QSOs between Portland Oregon and the Mississippi river.
Bill of Materials (BOM)
| Part Description | Model | Qty. | Unit Cost [$] | Total Cost [$] |
|---|---|---|---|---|
| 450 ohm Ladder Line | JSC #1318 | 20 ft. | 1.00 | 20.00 |
| RG-8X transmission coax cable | RG8X mini 8, UHF Connectors | 50 ft. | 0.50 | 25.00 |
| Balun Coax w/SO-239 Connector | Shireen RFC100A, 6ft. | 1 | 10.00 | 10.00 |
| Snap-On Ferrite Inductor | TDK ZCAT2035-0930A | 4 | 2.17 | 8.68 |
| Bonding Glue | Loctite Plastics Bonding | 1 | 3.88 | 3.88 |
| Total | 67.56 |